According to the state of the art, for the purpose of minimizing fuel consumption, powertrains for motor vehicles are frequently designed such that the main drive parts are driven in the direct gear. In the direct gear, the power flow occurs by way of direct coupling of the input shaft with the output shaft, which results in an increase in the degree of efficiency. By contrast, in the additional non-direct gears further losses develop, for example, due to gear meshing under load, dynamic anti-friction bearing load and pump power.
In transmissions in the direct gear, according to the state of the art, the power-conducting parts required for the remaining gears are not entirely uncoupled as is the case, for example, in the transmission of DE 198 31 293 A1 of the Applicant. Due to the fact that the countershafts are driven via a drive constant, the shafts, wheels, bearings, synchronizing parts, etc., each rotate along at the speed specified by the drive constant, although these parts are not involved in the power transmission process.
Due to the resulting friction, which also develops in the unloaded state, the degree of efficiency of the transmission deteriorates. The friction can be caused through churning losses caused by the immersion of the gear wheels in the oil pan or by friction losses on the synchronizations and on the bearings.
DE 41 17 642 A1 describes a multi-shaft transmission with several gear in which at least one gear is formed by a gear set, wherein the gear wheels of the gear set are rotatably seated on corresponding shafts and mesh on a continuous basis, and wherein each shaft comprises a clutch or synchronizing device in order to complete or interrupt the torque transmission path via the clutch. This way the gear wheels of the gear set can be isolated from the input and output so that the total inertia mass of the rotating gear parts is reduced. This design has the disadvantage that by using two synchronizing devices for one gear set the manufacturing and maintenance costs are negatively impacted.
It is the objective of the present invention to provide a transmission comprising an input shaft, an output shaft and at least one countershaft, which avoids the disadvantages of the state of the art and exhibits an optimized degree of efficiency in the direct gear.